The present invention relates to an overcharge prevention method and a charging circuit, suitable for preventing overcharge, and an electronic device and a timepiece, employing the overcharge prevention method and the charging circuit. This invention relates generally to a
In a charging circuit for charging a voltage storage device, such as a high-capacitance capacitor or a secondary battery, with an AC voltage generated by a generator, a diode-bridge circuit is typically employed as a rectifier circuit for full-wave rectifying the AC voltage. However, the diode-bridge circuit suffers from a loss due to a voltage drop through two diodes.
A compact and portable electronic device, such as a wristwatch, which employs a generator generating a small-amplitude AC voltage, is affected much by the loss through the diode-bridge circuit, and using the diode-bridge circuit as a rectifier circuit is not appropriate.
In view of the above problem, a synchronous rectifier circuit using transistors, rather than a diode, has been proposed.
FIG. 23 is a circuit diagram showing one example of a charging circuit employing a conventional synchronous rectifier circuit.
As shown in FIG. 23, the charging circuit includes comparators CMP1A and CMP1B, comparators CMP2A and CMP2B, P-channel FETs MP1 and MP2, N-channel FETs MN1 and MN2, and a high-capacitance capacitor C (charged device) for storing a charging current.
The comparator CMP1A compares an output voltage V1 at an input terminal AG1 connected to a generator AG with a source voltage Vdd. The comparator CMP1B compares an output voltage V2 at an input terminal AG2 connected to the generator AG with the source voltage Vdd.
The comparator CMP2A compares the output voltage V1 at the input terminal AG1 with a source voltage Vss. The comparator COM2B compares the output voltage V2 at the input terminal AG2 with the source voltage Vss.
The P-channel FET MP1 is turned on and off under the control of the comparator CMP1A, and the P-channel FET MP2 is turned on and off under the control of the comparator CMP1B.
The N-channel FET MN1 is turned on and off under the control of the comparator CMP2A, and the N-channel FET MN2 is turned on and off under the control of the comparator CMP2B.
D1-D4 are MOSFET parasitic diodes.
FIG. 24 is a timing diagram illustrating the operation of the above-referenced charging circuit.
The generator AG respectively outputs, at the input terminals AG1 and AG2, the output voltages V1 and V2 between which a phase difference of 180xc2x0 occurs. The P-channel FET MP1 is turned on by the comparator COM1A when the output voltage V1 of the generator AG becomes equal to or higher than the source voltage Vdd.
The N-channel FET MN2 is turned on by the comparator COM2B when the output voltage V2 of the generator AG becomes equal to or lower than the source voltage Vss. Similarly, the P-channel FET MP2 is turned on by the comparator COM1B when the output voltage V2 of the generator AG becomes equal to or higher than the source voltage Vdd, and the N-channel FET MN1 is turned on by the comparator COM2A when the output voltage V1 of the generator AG becomes equal to or lower than the source voltage Vss.
A charging current i flows from the generator AG through arrow-headed paths into the high-capacitance capacitor C, charging the high-capacitance capacitor C, when both the P-channel FET MP1 and the N-channel FET MN2 are on, and when both the P-channel FET MP2 and the N-channel FET MN1 are on. In this way, the synchronous rectifier circuit employing the transistors performs full-wave rectification.
In such a charging circuit, when the charging voltage for the high-capacitance capacitor C exceeds a predetermined voltage, an overcharge state occurs, degrading the charging circuit and dropping its charging efficiency.
The present invention has been developed in view of the above problem, and it is an object of the present invention to provide an overcharge prevention method, a charging circuit, an electronic device and a timepiece, for preventing overcharge and for preventing a shortcircuit of a voltage storage element associated with an overcharge prevention step.
According to a first aspect of the present invention, in an overcharge prevention method for a voltage storage element connected to a bridge rectifier circuit including a first switching section connected between one input terminal supplied with an AC voltage and a first power source line, a second switching section connected between the other input terminal supplied with the AC voltage and the first power source line, a third switching section connected between the one input terminal and a second power source line, and a fourth switching section connected between the other input terminal and the second power source line, both the first and second switching sections or both the third and fourth switching sections are concurrently turned on, forming a closed loop path between the one input terminal and the other input terminal.
In the present invention, the first and second switching sections are P-channel MOSFETs while the third and fourth switching sections are N-channel MOSFETs.
In the present invention, an overcharge prevention method is used in a charging circuit which rectifies an AC voltage supplied to input terminals to charge a voltage storage element with power, wherein the charging circuit includes a first comparator section for comparing a terminal voltage at one input terminal supplied with the AC voltage with an output voltage at a first power source line, a first switching section, which is connected between the first power source line and the one input terminal, and is turned on and off under the control of the first comparator section, a second comparator section for comparing a terminal voltage at the other terminal with the output voltage at the first power source line, a second switching section, which is connected between the first power source line and the other input terminal, and is turned on and off under the control of the second comparator section, a third comparator section for comparing the terminal voltage supplied to the one terminal with an output voltage at a second power source line, a third switching section, which is connected between the second power source line and the one input terminal, and is turned on and off under the control of the third comparator section, a fourth comparator section for comparing the terminal voltage supplied to the other input terminal with the output voltage at the second power source line, a fourth switching section, which is connected between the second power source line and the other input terminal, and is turned on and off under the control of the fourth comparator section, and the voltage storage element connected between the first power source line and the second power source line. The overcharge prevention method includes a detecting step for detecting the voltage charged at the voltage storage element, a determining step for determining whether the detected charge voltage exceeds a predetermined voltage, a turning step for turning off the first and second switching sections or the third and fourth switching sections, when the charge voltage exceeds the predetermined voltage, and a forming step for forming a closed loop path between the one input terminal and the other input terminal, by concurrently turning on the first and second switching sections or the third and fourth switching sections.
In the present invention, the determining step for determining whether the detected charge voltage exceeds the predetermined voltage includes a comparing step for comparing the charge voltage with a reference voltage, with the predetermined voltage being the reference voltage.
In the present invention, in the forming step for forming the closed loop path, both the first and second switching sections are turned on.
In the present invention, in the forming step for forming the closed loop path, the first and second switching sections are turned on, subsequent to turning off the third and fourth switching sections.
In the present invention, an overcharge prevention method includes a step for returning the third and fourth switching sections to a normal charging operation, subsequent to returning the first and second switching sections, when the first through fourth switching sections are returned to the normal charging operation.
In the present invention, in the forming step for forming the closed loop path, the first and second switching sections are turned on with the third and fourth switching sections remaining in an off state.
In the present invention, in the forming step for forming the closed loop path, the third and fourth switching sections are turned on.
In the present invention, in the forming step for forming the closed loop path, the third and fourth switching sections are turned on, subsequent to turning off the first and second switching sections.
In the present invention, an overcharge prevention method according includes a step for returning the first and second switching sections to a normal charging operation, subsequent to returning the third and fourth switching sections, when the first through fourth switching sections are returned to a normal charging operation.
In the present invention, in the forming step for forming the closed loop path, the third and fourth switching sections are turned on with the first and second switching sections remaining in an off state.
In the present invention, in the detecting step for detecting the voltage charged at the voltage storage element, the detection of the charge voltage is intermittently performed at a predetermined sampling period.
According to a second aspect of the present invention, a charging circuit includes first switching means connected between one input terminal supplied with an AC voltage and a first power source line, second switching means connected between the other input terminal supplied with the AC voltage and the first power source line, third switching means connected between the one input terminal and the second power source line, fourth switching means connected between the other input terminal and the second power source line, a voltage storage element connected to a bridge rectifier circuit including the first switching means, the second switching means, the third switching means, and the fourth switching means, and closed loop forming means for forming a closed loop path between the one input terminal and the other input terminal, by concurrently turning on the first and second switching means or the third and fourth switching means.
In the present invention, the closed loop forming means concurrently turns on the first and second switching means subsequent to turning off the third and fourth switching means, or turns on the third and fourth switching means subsequent to turning off the first and second switching means.
A charging circuit, for charging a voltage storage element arranged between a first power source line and a second power source line, with charge, by rectifying an AC voltage supplied between first and second input terminals, includes first comparator means for comparing a terminal voltage supplied to a first input terminal with an output voltage at a first power source line, first switching means, which is connected between the first power source line and the first input terminal, and is turned on and off under the control of the first comparator means, second comparator means for comparing a terminal voltage supplied to a second input terminal with the output voltage at the first power source line, second switching means, which is connected between the first power source line and the second input terminal, and is turned on and off under the control of the second comparator means, third comparator means for comparing the terminal voltage supplied to the first input terminal with an output voltage at a second power source line, third switching means, which is connected between the second power source line and the first input terminal, and is turned on and off under the control of the third comparator means, fourth comparator means for comparing the terminal voltage supplied to the second input terminal with the output voltage at the second power source line, fourth switching means, which is connected between the second power source line and the second input terminal, and is turned on and off under the control of the fourth comparator means, a voltage storage element, which is connected between the first power source line and the second power source line, and is charged with a charging current rectified through the first through fourth switching means, predetermined voltage comparator means, which detects a voltage charged at the voltage storage element and determines whether the detected charge voltage exceeds a predetermined voltage, and closed loop forming means which forms a closed loop path between the first input terminal and the second input terminal by turning off the third and fourth switching means and by turning on the first and second switching means, in response to the detection result by the predetermined voltage comparator means.
In the present invention, the predetermined voltage comparator means, regarding the predetermined voltage as a reference voltage, detects whether the charge voltage exceeds the reference voltage.
The closed loop forming means of the present invention includes first control signal generating means for generating a first control signal for turning on the first and second switching means when the predetermined voltage comparator means detects that the charge voltage exceeds the predetermined voltage, second control signal generating means for generating a second control signal for turning off the third and fourth switching means prior to turning on the first and second switching means, first gating means, connected between the first comparator means and the first switching means, for turning on the first switching means in response to the first control signal, second gating means, connected between the second comparator means and the second switching means, for turning on the second switching means in response to the first control signal, third gating means, connected between the third comparator means and the third switching means, for turning off the third switching means in response to the second control signal, and fourth gating means, connected between the fourth comparator means and the fourth switching means, for turning off the fourth switching means in response to the second control signal.
The closed loop forming means of the present invention further includes control signal generating means for generating a control signal for turning on the first and second switching means and for turning off the third and fourth switching means, when the predetermined voltage comparator means detects that the charge voltage exceeds the predetermined voltage, first gating means, connected between the first comparator means and the first switching means, for turning on the first switching means in response to the control signal, second gating means, connected between the second comparator means and the second switching means, for turning on the second switching means in response to the control signal, third gating means, connected between the third comparator means and the third switching means, for turning off the third switching means in response to the control signal, fourth gating means, connected between the fourth comparator means and the fourth switching means, for turning off the fourth switching means in response to the control signal, fifth gating means for supplying the first gating means with the control signal when the third switching means is in an off state, and sixth gating means for supplying the second gating means with the control signal when the fourth switching means is in an off state.
The switching means of the present invention is a transistor.
In the present invention, a parasitic diode is connected in parallel with the transistor.
In the present invention, the AC power supplied to the input terminals is generated by a generator which includes an oscillating weight that turns and a generating element for generating an electromotive force in response to the turn motion of the oscillating weight.
In the present invention, the AC power supplied to the input terminals is generated by a generator which includes an elastic member to which a deforming force is exerted, rotary means that is rotated by a restoring force that takes place when the elastic member restores an original shape, and a generating element that generates an electromotive force in response to the rotary motion of the rotary means.
In the present invention, the AC power supplied to the input terminals is generated by a generator which includes a piezoelectric element that generates an electromotive force by means of the piezoelectric effect in response to a displacement applied thereto.
In the present invention, the predetermined voltage comparator means intermittently detects a voltage charged at the voltage storage element at a predetermined sampling period.
According to a third aspect of the present invention, an electronic device includes a generator for generating an AC power, a charging circuit including first comparator means for comparing a terminal voltage supplied to a first input terminal with an output voltage at a first power source line, first switching means, which is connected between the first power source line and the first input terminal, and is turned on and off under the control of the first comparator means, second comparator means for comparing a terminal voltage supplied to a second input terminal with the output voltage at the first power source line, second switching means, which is connected between the first power source line and the second input terminal, and is turned on and off under the control of the second comparator means, third comparator means for comparing the terminal voltage supplied to the first input terminal with an output voltage at a second power source line, third switching means, which is connected between the second power source line and the first input terminal, and is turned on and off under the control of the third comparator means, fourth comparator means for comparing the terminal voltage supplied to the second input terminal with the output voltage at the second power source line, fourth switching means, which is connected between the second power source line and the second input terminal, and is turned on and off under the control of the fourth comparator means, a voltage storage element, which is connected between the first power source line and the second power source line, and is charged with a charging current rectified through the first through fourth switching means, predetermined voltage comparator means, which detects a voltage charged at the voltage storage element and determines whether the detected charge voltage exceeds a predetermined voltage, and closed loop forming means which forms a closed loop path between the first input terminal and the second input terminal by turning off the third and fourth switching means and by turning on the first and second switching means, in response to the detection result by the predetermined voltage comparator means, and a processing circuit operated from the power supplied by the voltage storage element.
In the present invention, the predetermined voltage comparator means, regarding the predetermined voltage as a reference voltage, detects whether the charge voltage exceeds the reference voltage.
In the present invention, the predetermined voltage comparator means intermittently detects a voltage charged at the voltage storage element at a predetermined sampling period.
According to a fourth aspect of the present invention, a timepiece includes a generator for generating an AC power, a charging circuit comprising first comparator means for comparing a terminal voltage supplied to a first input terminal with an output voltage at a first power source line, first switching means, which is connected between the first power source line and the first input terminal, and is turned on and off under the control of the first comparator means, second comparator means for comparing a terminal voltage supplied to a second input terminal with the output voltage at the first power source line, second switching means, which is connected between the first power source line and the second input terminal, and is turned on and off under the control of the second comparator means, third comparator means for comparing the terminal voltage supplied to the first input terminal with an output voltage at a second power source line, third switching means, which is connected between the second power source line and the first input terminal, and is turned on and off under the control of the third comparator means, fourth comparator means for comparing the terminal voltage supplied to the second input terminal with the output voltage at the second power source line, fourth switching means, which is connected between the second power source line and the second input terminal, and is turned on and off under the control of the fourth comparator means, a voltage storage element, which is connected between the first power source line and the second power source line, and is charged with a charging current rectified through the first through fourth switching means, predetermined voltage comparator means, which detects a voltage charged at the voltage storage element and determines whether the detected charge voltage exceeds a predetermined voltage, and closed loop forming means which forms a closed loop path between the first input terminal and the second input terminal by turning off the third and fourth switching means and by turning on the first and second switching means, in response to the detection result by the predetermined voltage comparator means, and a time measurement circuit, operated from the power supplied from the voltage storage element, for measuring time.
The predetermined voltage comparator means of the present invention, regarding the predetermined voltage as a reference voltage, detects whether the charge voltage exceeds the reference voltage.
The predetermined voltage comparator means of the present invention intermittently detects a voltage charged at the voltage storage element at a predetermined sampling period.